Impregnated sheet product



Patented May 15, 1934 UNITED I STATES PKATENTI OFFICE 1,958,976IMPREGNATED SHEET raonoc'r George A. Richter, Berlin, N. H., assignor toBrown Company, 'Berlin, N. H., a corporation of Maine No Drawing.Original application December 11,

1931, Serial No. 580,496.

Divided and this application November 4, 1932, Serial No. 641,317

2 Claims. (01. 92-40) The subject of this invention is the manufactureof impregnated sheet products whereinnovel types of prefabricatedfibrous webs serve as" capable of undergoing impregnation with aqueousdispersions of binders like rubber latex, are intended for impregnationwith impregnants that can be introduced into the web in heat-liquefiedcondition and then caused to set or congeal as a continuous phaseimparting thereto such desired properties as body, stiffness, strength,tear resistance, mouldability, water-repellency, and weatheringcapacity) 3 In making certain types of impregnated sheet products, it iscustomary practice to start with a suitable prefabricated fibrous weband to immerse the web in a bath of heat-liquefied im-.

pregnant of sufficient fluidity to enter into and through the web andthen to remove the web fromthe bath and cause the impregnant to set orharden to its normally solid state. Such, for example, is the practicein making waterproof sheet products for roofings, flooring, and"building purposes, a bath of molten asphalt or other bitumenconstituting the medium into which the starting web is dipped. Such isalso the practice inmaking shoe stiffener material of the so-calledthermoplastic variety, which is prepared by impregnating asuitable'falbric with molten compositions, such as rosin or the iike,which upon setting impart stiffness and resiliency to the impregnatedsheet. The shoe stiffener blanks cut from the impregnated sheet aresoftenable and mouldable under the application of moderate heat non-injurious to leather, wherefore they can be moulded into the desired shapeduring assembly with the shoe upper, and then allowed to stiflen in suchshape. A

In accordance with thepresent invention, I prepare a waterlaid fibrousweb preeminentiy serviceable as a carrier fo r an impregnant, and moreespecially one which is to be associated in a molten state with suchweb. There are factors which I have found .to be of great importance inpreparing the web of the present invention, especially whencomparatively shortfibred cellulose fibers, such as wood pulp, areemployed as the raw material on account of their 'low cost and easyavailability. Thus, I have found that one should not strive primarilyfor the se- .,cdi'idition from the paper machine.

cur ement of a strong web as it comes off in dry On the contrary, onemay advantageously deposit the web from the aqueous fiber suspension andthen dry it with the application of little, if any, outside pressureeither-during forming or drying. Other than the drawingtogether of thefibers on account of the action of surface tension during drying, theweb may, therefore, be in practically the same condition of compactnessas deposited from aqueous suspension with its fibers only looselyinterfelted. The web may hence be tender or lacking in much tensilestrength, but it may me fluffy or bulky and so highly porous andabsorbent that it can readily take up far more than its own weight inmolten asphalt or other liquid impregnant. In making the webs of thepresent invention, I use substantially unbleached, preliberatedcellulose pulps as raw material, preferably substantially unbleachedwood pulps, such askraft or sulphite, or mixtures of such pulps.Preferably, also, these wood pulps, although substantially unbleached,have undergone refining to a higher alpha cellulose content than thatassociated with the raw pulp liberated from the wood. The refiningtreatment may be carried out win a suitable alkaline liquor underconditions alpha-cellulose content of, say, about 93% to 96%, as is nowknown to those skilled in the art. These raw or refined pulps insubstantially unbleached condition are preferably used in practicallyunbeaten or unhydratedform in making the webs of the present invention,as beating not only shortens the fibers but generates cellulose hydrateand thereby detracts from theabsorbency in the resulting web, eventhough it makes for greatest tensile strength in the web. As alreadyindicated, however, I am not primarily interested in securing a web ofinitial high strength at the sacrifice of web absorbency, for reasonswhich will presently appear.

I have found that webs made as hereinbefore described are far superiorto the kinds of webs heretofore used as the carriers for heat-liquefiedimpregnants. Heretofore, waterlaid webs were prepared with a viewtoward'securing considerable initial strength in the web at the expenseof web absorbency. I have found, however, that the waterlaid webs of thepresent invention are so highly absorbent that, despite their lowinitial strength, they can be drawn continuously through one or morebaths of heat-liquefied impregnants, e. g., molten asphalt, without'muchtrouble on account of breakage. I attribute this success to same pulpswere in substantially unbleached condition. Consequently when, as istrue of my web,.

and diffuses throughout the web, thereby serving.

to bind together the fibers so that the web immediately upon enteringthe bath is so greatly strengthened that it can endure the furtherstresses in its journey without rupturing. I attribute this success alsoto the substantially unbleached state of the fibers and, if they havebeen refined, further to their high alpha cellulose content. Inunbleached state, the fibers are notably freer from oxycelluloses orother degraded celluloses which are unstable, especially underapplication of heat. This applies especially to raw pulps, but it holdstrue even in connection with refined pulps. Under the application ofconsiderable heat, bleached pulps may lose much more of their strengththan would bethe case if the it is made up of unbleached pulp fibers, itis not weakened appreciably in passing through a bath of hot, liquidimpregnant. Moreover, unbleached pulps invariably yield ffreer aqueouspulp sus pensions than do similar bleached pulps whose oxycellulosecontent apparently becomes more or less suspended asc-fine or colloidalparticles in the water of suspension, especially under agitation.The'unbleached pulp suspension which I use enhances the porosity of theresulting web, for freeness in a pulp suspension is consonant withporosity in the web derived therefrom, whereas slowness in the pulpsuspension makes for density in the web. When the web is made fromunbleached, refined pulp, it is especially resistant to being weakenedby heat on account of the higher proportioncf heat-resisting alphacellulose in the refined pulp fibers. Moreover, the refined pulp fibersalso conduce to a web of enhanced absorbency by virtue of the greaterfreeness possessed by refined pulps as compared with similar unrefinedpulps.

Any one of the species of webs made in accordance with the presentinvention can imbibe more than 250% of its own weight in molten asphalt,

without having a supertluity of asphalt on its sur-- faces. Thisimbibition of asphalt may take place .even more rapidly than when websof lower asphalt-holding capacity, such as heretofore made, are treatedto the limit of their capacity. accordingly, the webs of the presentinvention need be in contact with the heat-liquefied asphalt for ashorter period of time, to attain a given asphalt content. There is thusless danger of scorching the fibers and causing their embrittlement.

Non-cellulosic fibers, especially those like wool and asbestos, whicharemore resistant to heat than cellulose fibers, may be blended with theaqueous suspension of cellulose pulp used in fabricating my web. Thecellulose pulp may be preliberated wood pulps or longer-fibered pulps,such as derived from manila, sisal, ramie, or the like,

or mixtures of such pulps. Wood pulps offer the advantage of low costand easy availability, but the blending with such pulps of thelongerfibe'red pulps derived from manila, sisal, ramie,

' or the like is desirable, in that the web attainable from such a blendhas higher initial strength. A portion of the pulp may be mercerized, asmercerized fibers appreciate the-porosity and bulkiness of the web,although it is preferable to use a substantial portion, if not most, ofthe pulp in 'unmercerized condition, because of the difllculty inrealizing a web of good formation or texture from a pulp furnishmercerized in entirety.

I shall now give anexample of procedure practised in accordance with thepresent inventionto produce a bituminized web designed for roofing,building, and analogous purposes. I can take as raw material a kraftpulp which has been refined to an alpha cellulose content of about 93%to about 96%, but which is in essentially unbleached condition. The pulpis suspended in practically unbeaten condition in water to form ahomogeneous dilute suspension, which is run off on a paper machineoperated under conditions leading to a dry web having a compactnessfalling within the range of about 30 to 55. This means that in someinstances, there must be lita tie, if any, pressure applied to thewebduring its traverse of both the wet and dry ends of the paper machine.Yet, in attaining felts having a compactness at the upper end of therange hereinbefore given, it may be necessary to compact or condense thefelt more or, less during its fabrication on the felt-making machine.Felts whose compactness lie at the upper end of the range are of greatvalue in making bituminized sheets for fioorings, where highmouldability, stretchability, and yieldability under distorting ordenting influences are undesirable qualities. Felts intended forbituminized roofings, on the other hand, may have a compactness lying atthe lower end of the range, sin'cein such case it is desired that thefelts imbibe during impregnation a maximum amount of bitumen or asphalt..'I'he.com-' pactness values given are obtained by dividing the basisweight. in pounds by the thickness in inches and multiplying by thefactor 10". The expression basis weight, as known in papermakingcircles, represents the weight in pounds of 480 sheets whose dimensionsare 24x36 inches,

thisbeing equivalent to 2880 square feet of sheet material. In otherwords, the compactness value really represents the weight of fiber perunit volume of sheet material. The dry starting web thus producedis'tender and tears readily under much stress. Nevertheless, it canundergo bituq minization satisfactorily as a continuous sheet by runningit through one or more baths of molten asphalt, for instance, air-blownasphalt having a,

melting point of about 150 F. (ball and ring test) and heated to about300 to 350 F. The

stretch of webin contact with the fluid asphalt surface, that is, onefree from superfluous asphalt,

after the continuous phase carried by the web has been allowed or causedto congeal or set. Impregnation may be carried out under otherconditions, but in each case the contact of web with the fluid asphaltis coordinated with a web speed such that a uniformly and completelyimpregnated product is secured. i

The resulting product has high moisture and weather resistance, whichproperties are traceable to the high proportion of asphalt presenttherein as a continuous phase. The high asphalt-to-fiber.

ratio reduces the cost of the finished product on a pound basis, becauseasphalt is considerably cheaper than fiber. markably high resistanceagainst, tearing, especially against the initiation of tear, that thetender starting web would hardly be associated in ones mind with such'adifferent product. Be-

cause the product contains a refined, substantially unbleached woodpulwitstands up against The producthas such rethe action of moisture andweathering, by reason of the high stability of the fibers, as well as oftheir complete encasement by asphalt.

The foregoing exemplary procedure, with only a change in the materialused as an impregnant, can serve in the manufacture of thermoplasticshoe stiffener material for cutting into shoe stifiener blanks, e. g.,box toe blanks. In place of the bath of asphalt, a suitablethermoplastic stiiiening composition, like rosin, should be used at atemperature of, say, about 250F. This temperature is sufficient toliquefy the rosin to a fluency ensuring quick and uniform impregnationof the web. If desired, the asphalt may be blended in the proportion of,say 50% with the rosin, in which case the temperature of the bath ofmixed impregnant may be raised to, say, about 300 to 320 F. Theimpregnated web can be cut up into shoe stiffener blanks, which arecharacterized by their excellent moulding properties under theapplication of heat moderate enough not to injure leather. Not only dosuch blanks lend themselves to moulding in heat-softened condition tothe desired shape in the shoe, but

they are superior to the article heretofore made. Their excellence forthis purpose is evidenced by l the fact that they can be nicely mouldedeven about sharp edge corners while in heat-softened condition and thencaused to set in such shape without subsequently tending to undergodeformation.

It is to be observed that the impregnated products for which the webs ofthe present invention serve as foundations are not in any waydepreciated on account of the unbleached state of the fibers, as thefibers are masked by impregnants of the character of molten asphalt,rosin, or the like, or by aqueous dispersions of binders, such as rubberlatex, asphalt, or colored waxes, which are dried out in the web tocoalesce the dispersed particles as a continuous phase.

By the expression pm-liberated cellulose pulp as used in thespecification, I means a pulp which,

like wood pulp, has been liberated by a previous digestion of wood orother fiber-bearing raw mae terial in any suitable liquor capable ofisolating the fibers as a pulp from the cementitious material bindingthem together in the raw material. It is thus seen that the expressionis exclusive of cotton fibers or rag pulps which must undergoconsiderable beating to become converted into a suitable half-stock.Besides, virgin cotton fibers carry waxes on their surfaces, whichdetract from their absorbency.

This application is a division of my application Serial No. 580,496,filed December 11, 1931, which in turn is a continuation in partof myapplication Serial No. 175,946, filed March 16, 1927, now Patent No.1,891,027, dated December 13, 1932.

I claim:

1. A process which comprises making a waterlaid felt from a furnishcontaining mercerized cellulose pulp, and impregnating the felt with anon-cellulosic binder in amount by weight at least equal to thedryweight of the felt. r

2. A waterlaid felt made from a fiber furnish containing mercerizedcellulose pulp and impregnated with a non-cellulosic binder in amount byweight at least equal to the dry weight of the felt.

, GEORGE A. RICHTER.

